Extractor pump for transmission fluid "flush"?

I could see the detergent washing the incidental nonferrous stuff off the magnet but I don’t see how detergent will cause magnetic ferrous material to be released from the magnet.

Other than that part, it makes sense. I think in most cases flushing is a bad idea. The process of removing the pan to inspect and clean before making a flush decision about flushing sounds like a good idea. If I were going to flush one rather than a drain and fill I would use the process above.